The present invention relates to a non-contact, opto-electronic method of determining the surface shape of a curved, formed sheet of glass to a useful precision, and for analyzing optical distortion occurring in such formed glass sheets.
Glass forming processes, typically, involve heating a glass sheet or panel to, or near, its softening temperature, and then forming the glass to a desired configuration by, for example, gravity bending or press bending. Such heating and forming operations have the potential to create physical and optical defects in the glass sheet or panel, for example deviation from the desired configuration and/or optical distortion. Particular types of non-obvious physical glass defects may cause problems with subsequent processing of the formed glass sheet and/or may pose difficulties when, for example, such formed glass sheet is a vehicle window, and it is being installed in a vehicle body opening at a vehicle assembly plant. Reflected optical distortion may also be unacceptable to vehicle manufacturers, and may be annoying to vehicle drivers/passengers. It would be desirable to have an automated system to determine glass surface shape as well as being capable of objectively assessing optical distortion in shaped glass sheets or panels, in order to minimize formed glass sheets having such non-obvious physical and/or optical defects, enter the stream of commerce.
Automated systems purported to detect and measure physical and optical defects in formed glass sheets or panels are the subject of many U.S. patents. For example:
U.S. Pat. No. 5,067,817 describes a method and apparatus for measuring the curvature and profile of a reflective test surface by simultaneous measurement of slope at two closely spaced points on the test surface.
U.S. Pat. No. 5,085,516 describes a method and apparatus for comparing the shape of the edges of a curved object being monitored, with the shape of standard curved object. An application of the method and apparatus is said to be monitoring of window panels in the automobile industry.
U.S. Pat. No. 5,568,258 describes a method of measuring distortion of a transmitting beam, characterized in that, a transmitting beam is emitted from a beam generator and projected onto a screen as a bright spot, the bright spot is scanned over the surface of the screen, and distortion of the transmitting beam is measured on the basis of a distance between a first location of the bright spot at a first time when the transmitting beam is incident on a beam receiving device, in a specified incident direction, upon being transmitted through a measured body, and a second location of the bright spot on the screen at a second time when the transmitting beam is incident on the beam receiving device in the specified incident direction, but the transmitting beam is not transmitted through the measured body.
U.S. Pat. No. 6,122,065 describes an apparatus and method for detecting surface defects on an article freely standing on a conveyor, which generates profile trace data corresponding to profile trace at a cross-section of the article. A surface shape inspection unit comprising an optical ranging system using a laser and a camera for obtaining the profile trace data through triangulation-based derivation techniques.
U.S. Pat. No. 4,853,777 describes a system to quantitatively determine the short-term and long-term waviness of a smooth surface by impinging light radiation, namely laser light, onto the surface, detecting the resultant light image and mathematically processing the subject light image.
U.S. Pat. Nos. 6,376,829 and 6,433,353 describe a method and apparatus for detecting front surface irregularities in a glass plate. More specifically, the method described involves irradiating a beam of light toward a surface of a transparent plate at an angle of incidence between 86° and 89°, or 60° to 89° after such light beam is polarized (“P” or “S”-polarized) by a polarizing element between the light beam source and the transparent plate. A reflected image from a front surface of the transparent plate is then projected on a screen, is inspected by one of several possible methods, whereby density signals said to be representative of the reflected image are analyzed to calculate the irregularities present on the surface of the transparent plate.